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Stellarator

A stellarator is a device that confines plasma by using external coils alone to create a twisted magnetic field. Unlike a tokamak, it does not require a plasma current for confinement.

Simple Definition (High School)

Section titled “Simple Definition (High School)”

Whereas a tokamak drives a current through the plasma itself to create the twist in the magnetic field, a stellarator builds coils with a complex twisted shape from the start, completing the magnetic field needed for confinement using the coils alone. It was conceived in 1951 by Lyman Spitzer of Princeton University, who named it for its aim of creating a “stellar” (star-like) device.

How It Works (Undergraduate and Above)

Section titled “How It Works (Undergraduate and Above)”
  1. Three-dimensionally twisted external coils (helical coils or modular coils) generate a magnetic field with rotational transform entirely on their own
  2. Because there is no need to drive a large current through the plasma, the device is in principle well suited to steady-state operation
  3. Since the magnetic field has a three-dimensional shape, there is great freedom in design, but the difficulty of computation and fabrication is also high

Advantages

Section titled “Advantages”
  • Steady-state operation is possible (no reliance on an induced current)
  • No disruptions arising from plasma current
  • Operational control is relatively simple

Challenges

Section titled “Challenges”
  • The coil shapes are complex, making them difficult and expensive to manufacture
  • Neoclassical transport arising from the three-dimensional magnetic field must be optimized
  • Historically it lagged behind the tokamak in confinement performance (rapidly improving with optimized design)

Representative Devices

Section titled “Representative Devices”
  • Wendelstein 7-X (Germany, optimized modular coil scheme)
  • LHD, the Large Helical Device (Japan, heliotron scheme)
  • HSX (USA, quasi-helically symmetric configuration)

Learn More

Section titled “Learn More”
Section titled “Related Terms”